Proportional temperature control device

ABSTRACT

A device for maintaining a relatively constant temperature in an enclosure has a polyconductor connected in parallel to a first resistance element within the enclosure to be heated. The polyconductor is connected in series to a second resistance element located outside of the enclosure and this circuit is connected to a source of current which will cause the first resistance element to heat the enclosure as current passes therethrough; when the transition temperature of the polyconductor is reached, the first resistance element is shunted by the change in conductive state of the polyconductor and heating thereby is proportionally reduced in order to maintain the temperature within the enclosure at the transition temperature of the polyconductor.

United States Patent 191 Kahn [ PROPORTIONAL TEMPERATURE CONTROL DEVICE[75] Inventor: David Kahn, Harrisburg, Pa.

[73] Assignee: AMP Incorporated, Harrisburg, Pa.

[22] Filed: May 4, 1973 [21] Appl. No.: 357,319

[52] US. Cl 219/210, 219/505, 307/310,

338/23, 338/25 [51] Int. Cl. H05b 1/00 [58] Field of Search 219/209,210, 501, 505,

[451 Mar. 19, 1974 Primary Examiner-C. L. Albritton [57] ABSTRACT Adevice for maintaining a relatively constant temperature in an enclosurehas a polyconductor connected in parallel to a first resistance elementwithin the enclosure to be heated. The polyconductor is connected inseries to a second resistance element located outside of the enclosureand this circuit is connected to a source of current which will causethe first resistance element to heat the enclosure as current passestherethrough; when the transition temperature of the polyconductor isreached, the first resistance element is shunted by the change inconductive state of the polyconductor and heating thereby isproportionally reduced in order to maintain the temperature within theenclosure at the transition temperature of the polyconductor.

13 Claims, 1 Drawing Figure 6.3 AC (or DC) 5 6 References Cited UNITEDSTATES PATENTS 3,440,397 4/1969 Vesper et a1 219/501 X 3,322,982 5/1967Craiglow et 211.... 3,419,214 12/1968 Evalds 219/501 X 1 WATTPAIENTEDMARIQ I974 37989413 6.3 AC (or DC) IO .(1 I WATT PROPORTIONALTEMPERATURE CONTROL DEVICE perature at the selected or desired level.Moreover, al-.

though the technology with respect to bimetallic temperature controldevice is quite advanced, such devices are still relatively inaccuratein operation and cannot precisely control temperatures to the degree ofaccuracy required in certain applications.

More specifically, many electronic devices utilize temperature sensitivequartz crystal elements as oscillators. Such elements must be maintainedat selected predetermined temperatures in order for them to produce thedesired frequency ofoscillation. If the temperature surrounding suchcrystals varies, then the frequency of oscillation produced thereby willalso be varied. This is undesirable, particularly in precisionelectronic equipment such as radios and the like. To overcome theeffects of heat fluctuations in the surroundings, such crystals aretypically maintained within their own separate enclosure with acontrolled heating element used to maintain the selected temperaturearound the crystal. However, the maintenance of the temperature at theselected temperature level is extremely difficult and previouslyproposed bimetallic control elements have not been entirely satisfactoryfor this purpose.

Accordingly, it is an object of the present invention to provide atemperature control element which will maintain the temperature withinan enclosure at a relatively constant level.

Yet another object of the present invention is to provide a device forproportionately controlling the temperature within an enclosure.

Another object of the present invention is to provide a relativelysimple and inexpensive device for controlling the temperature level inan enclosure.

In accordance with the present invention a temperature control device isprovided for maintaining a predetermined temperature level in chamber,and in particular, within a chamber that contains a quartz crystaloscillating element for an electronic device. The control element of theinvention utilizes an advantageous feature available in recentlydeveloped materials commonly referred to in theart as polyconductors.These polyconductors are made in variety of compositions and have thepeculiar characteristic of exhibiting metallic electrical conductivityabove and little or no electrical conductivity below a predeterminedtransition temperature. That is, these materials typically have arelatively high resistance value when their temperature is below theircritical transition temperature while, on the other hand, attemperatures above their transition temperature, they have resistancevalues which are several orders of magnitude lower; for example, onethousandth of their resistance value below the transition temperature.Moreover, the high to low resistance transformation, and the reverse lowto high resistance transformation of these materials is achieved simplyby varying their temperature and can be repeated an infinite number oftimes. Another characteristic of these elements is that thetransformation from the high to low resistance state occurs relativelyabruptly at the transition temperature over a span of approximately 1C.In the course of this one degree span, the resistance value of theelement transforms proportionately to the temperature.

A number of such polyconductors and processes for doping the conductorsin order to adjust the desired transition temperature thereof aredisclosed in US. Pat. Nos. 3,402,131 to Futaki et al. and 3,532,641 toChamberland. In addition to the polyconductors disclosed in thosepatents, numerous other types of polyconductors are available, each ofwhich has a transition temperature at which the element abruptly changesits electrical property, being relatively non-conductive below thetransition temperature T and being electrically conductive above thetransition temperature.

In the illustrative embodiment of the present invention these negativetemperature-resistance characteristics of polyconductors areadvantageously used in combination with a first electricalresistance-heating element which is connected to a source of current inorder to maintain a constant temperature within an enclosure for aquartz crystal oscillator. The polyconductor is connected in parallel tothe electrical resistance heating element and both elements arecontained or positioned within the enclosure for the quartz crystal. A

source of current is connected through a resistance ele ment to theparallely connected polyconductor and heating resistance element inorder to supply current to the heating element to heat the latter inaccordance with Joules law. A second resistance element is connected inseries to the polyconductor, but is located outside of the enclosure forthe quartz crystal. As a result of this arrangement, the firstelectrical heating element raises the temperature within the enclosurefrom ambient as current flows therethrough. Because of the relativelyhigh initial resistance value of the polyconductor element within theenclosure, substantially all of the current passes through theresistance heating element so that heating occurs relatively rapidly.Ultimately, the temperature within the enclosure reaches the transitiontemperature of the polyconductor and the latter then becomes conductive.As this occurs, less current passes through the heating resistanceelement, so that its temperature decreases, thereby permitting theinterior of the enclosure to cool slightly. The cooling of the enclosurecauses the resistance of the polyconductor to increase, causing morecurrent to flow through the resistance heating element thereby increasing the temperature within the enclosure. Thus, there is a cyclicoperation between the polyconductor and the heating resistance elementwhich maintains the temperature of the enclosure at a relativelyconstant level corresponding to the transition temperature of thepolyconductor. However, it is noted that because the polyconductortransition from its high resistance to its low resistance state occursover a span of approximately 1C, and because the transition isrelatively proportional within that one degree span, the control of thetemperature within the enclosure is proportional rather than simplyon-off. As a result, the temperature control is proportional at thetransition temperature and a relatively level temperature can bemaintained within the enclosure.

The above, and other objects, features and advantages of this inventionwill be apparent in the following detailed description of anillustrative embodiment thereof which is to be read in connection withthe single FIGURE of the accompanying drawings which shows a schematiccircuit diagram of the temperature control device of the presentinvention.

As shown in the drawing in detail, a temperature control device 10,constructed in accordance with the present invention, includes a sourceof current 12 to which a heating and temperature control circuit 14 isopertively connected. Circuit 14 includes a first resistance heatingelement 16 located within an enclosure 18 (shown in phantom lines in thedrawings) which contains a quartz crystal oscillator element (not shown)such as is used in radios or other electronic equipment.

A polyconductor element 20 is electrically connected in parallel toresistance heating element 16 and is located within the chamber 18adjacent to the resistance element. An additional resistance element 22is electrically connected in series to the polyconductor element 20, butis located outside of the enclosure 18. The resistance element 22 has aresistance which may be larger or smaller than the resistance value ofelement 16, for purposes described more fully hereinafter. Finally, thepolyconductor 20 and the resistance element 16 are connected to currentsource 12 through an additional resistance element 23 which is alsolocated outside of enclosure 18.

Polyconductor 20 preferably is formed of a material selected as any oneof any of the materials in the group of polyconductor materialsexhibiting a negative temperature-resistance characteristic wherein thematerial abruptly transforms from a semi or nonconductive state to anelectrically conductive state at or above a transition temperature. Theterm polyconductor as used in this application and in the followingclaims is intended to mean any material exhibiting this desirablecharacteristic, i.e. exhibiting an abrupt transition between arelatively non-metallic conductivity to metallic conductivity at aspecific temperature. This abrupt transition normally takes place withina relatively small temperature range of approximately 1C, and thetransition within that one degree span is proportional to thetemperature variation within the span.

Materials within the definition or the term polyconductor as used inthis specification that exhibit these characteristics include, but arenot limited to V0,, V203, V407: V509 V8011 V8015! V6013 z a 8 a Ti O NbOFe O,, NiS, CrS, FeS, FeSi CrN. Each of these materials exhibits thenegative temperatureresistance characteristic, i.e. the transitionbetween relatively non-conductive and relatively conductive states atdifferent transition temperatures T Typically, the polyconductor 20 isformed from crystals of these materials in the shape of a disk orcylindrical rod having electrical contacts secured to opposite ends orsides thereof for electrically connecting the polyconductor to thecircuit.

In the illustrative embodiment of the present invention polyconductor 20is formed of V0 and has a transition temperature within the range of Cto 80C. The specific transition temperature can be selected or adjustedby doping the V0 material with metals or fluoride in the mannerdescribed in the above-identified patents. Preferably, the polyconductorhas a resistance value below its transition temperature which issubstantially higher than the resistance value of resistance heatingelement 16. This resistance value may also be adjusted, withouteffecting the transition temperature of the polyconductor, by adding ormixing with the polyconductor materials small amounts of a material suchas carbon or carbon compounds. The added material will increase theconductivity of the polyconductor below its transition temperature; thusthe resistance value of the polyconductor can be adjusted as desired byadding more or less of the carbon compound material as required.However, the resistance value is preferably selected such that below thetransition temperature of the polyconductor the total of thepolyconductor resistance and the resistance of resistor 22, outside ofthe chamber 18, is substantially greater than the resistance value ofthe resistance heating element 16; while on the other hand, above thetransition temperature this total is comparable to or approximately thesame as the resistance value of the heating resistor 16.

By selecting the respective resistance values of the elements in thismanner, when current from source 12 is supplied to circuit 14, through aswitch or the like (not shown) the current will initially flow throughresistance element 16, causing the same to be heated in accordance withJoules law and thus raising the temperature within chamber 18.Substantially all of the current will pass through the resistanceelement 16 because of the high resistance value of polyconductor element20 below its transition temperature. However, once the transitiontemperature of the polyconductor element is reached, the polyconductorwill switch to its high conductivity or low resistance state, so as toshunt the resistance element 16. As a result, there will be asubstantially smaller current flow through the element 16, and thatelement will produce less heat and will decrease in temperature. Thetemperature within the chamber 18 will then correspondingly decrease,causing polyconductor 20 to revert to its high resistance value and theheating element to increase in temperature. Accordingly, a control cycleis provided by the combination of the polyconductor and heatingresistance element 16 in the manner shown in the drawing, so that thetemperature within the chamber 18 is held at the transition temperatureof the polyconductor.

An advantageous feature of the present invention is the fact that therelatively abrupt transition of the polyconductor from its highconductivity state to its low conductivity state occurs over atemperature span of approximately 1C, and in that temperature span thechange in resistance value of the polyconductor is proportional. As aresult, the control of heat produced by resistor 16 is proportional,rather than a simple onoff control of the resistor as would be the casewith a conventional switch or bimetallic element. That is, once thetemperature within chamber 18 reaches the transition temperature of thepolyconductor, the resistance of the polyconductor over the 1C spandecreases proportionately to further increase in temperature. As theconductivity of the polyconductor decreases in this manner, the currentflow through the resistor 16 also decreases proportionately, therebyproportionately reducing the amount of heat provided by that element. Asthe temperature within chamber 18 falls because of the smaller amountsof heat produced by resistance element '16, the polyconductor resistanceproportionately increases, causing increased heat to be produced by theelement 16, raising the temperature within the enclosure 18. Thisfluctuation in the resistance value of polyconductor and the heatproduced by resistance element 16 will occur within this 1C span of theresistance transition of the polyconductor so that the temperaturewithin the enclosure 18 is controlled and maintained at that level, i.e.within the 1C span of the transition of the polyconductor. Accordingly,the temperature within the enclosure is held relatively constant and thewide fluctuations in temperature which occur with previously proposeddevices is avoided.

In one illustrative embodiment of the present invention which has beenproduced and tested, a satisfactory operating temperature control devicehas been provided wherein the voltage source 12 provided a voltage of6.3 volts, while resistance 16 had a resistance value of 7 ohms andresistance 22 had a value of 6 ohms. In that embodiment of the inventionthe polyconductor was'formed as a disk of V0 crystallites having asurface area on opposite sides thereof of approximately two millimeterssquare and a resistance value at temperatures below T of 700 ohms. Inaddition the resistance 23 had a value of 10 ohms. Because of thetransition characteristics of the V0 polyconductor, the polyconductor inthis embodiment had a resistance value above the transition temperaturesuch that the sum of its resistance value and the resistance value ofresistor 22 was less thanvthe 7 ohm resistance value of resistor 16above the transition temperature. In this connection, the resistancevaluesof resistor 22, as mentioned, may be higher or lower than thevalue of resistor 16. The specific value selected is chosen to control adesired rate of heat production by resistor 16. Thus, the

higher the resistance value of resistor 22, the higher the rate of heatproduced by resistor 16, above T since more current will flow throughresistor 16. On the other hand, decreasing the value of resistor 16 willdecrease the rate of heat production by resistor l6,above T since thecurrent flow through resistor 22 will be decreased.

Accordingly, it is seen that a relatively simple and inexpensivelymanufactured device is provided which products an accurate control oftemperature within an enclosure. The device can be used over a widerange of voltages and currents, with the values of the resistors and thetype of polyconductor used being varied accordingly in order to achievethe desired results. The polyconductor acts as a proportional controldevice which proportionately controls the amount of heat pro duced byresistor 16 within the enclosure 18 in order to maintain the temperaturewithin the enclosure at a relatively constant level. The polyconductorthus acts somewhat ,as a switch, but uses no moving parts in order toproduce the desired results. Accordingly, the device has a relativelylong life and is extremely durable in use while accurately controllingthe desired temperature. Therefore, it is particularly adapted for manyapplications where it is necessary to accurately maintain thetemperature within an enclosure at a specific level over an extendedperiod of time.

Of course, it is also to be understood that while the present inventionhas been described particularly for use in maintaining the temperatureof an enclosure for a quartz crystal oscillator, it can be used in otherappliand that various changes and modifications may be effected thereinby one skilled in the art without departing from the scope or spirit ofthis invention.

What is claimed is:

1. A proportional temperature control device adapted to be connected toa source of current to produce a temperature control cycle formaintaining the temperature in an enclosure at a relatively constantlevel, said device comprising a first electrical resistance element insaid enclosure for heating the interior of the enclosure when connectedto said source of current, a polyconductor connected in parallel withsaid first electrical resistance element in said enclosure, and a secondresistance element located outside of said enclosure and connected inseries with said polyconductor whereby, when said first resistanceelement is connected to said source of current said first resistance element is heated, in accordance with Joule s law, thereby raising thetemperature within said enclosure and of said polyconductor until thetransition temperature of the latter is reached, whereupon saidpolyconductor becomes increasingly conductive and increasingly shuntssaid first resistance element to permit said first resistance element,said enclosure and said polycon ductor to cool, thereby increasing theresistance of the polyconductor and allowing said first resistanceelement to produce increased heat and repeat the temperature controlcycle; said second resistance element having a resistance value which isless than that of said first resistance element, and said polyconductorbeing selected to have a resistance value below its transitiontemperature which is substantially higher than that of said firstresistance element and a resistance value above its transitiontemperature which is at least several orders of magnitude less than itshigher resistance value whereby the sum of the resistances of saidpolyconductor and said second resistance element above said transitiontemperature is comparable to the resistance value of said firstresistance element.

2. The device as defined in Claim 1 wherein the transition of saidpolyconductor from its high resistance value to its low resistance valueis abrupt, occurs over a temperature span of approximately 1C, and isproportional within that span, whereby the shunting of said firstresistance element is proportional within said span to proportionallycontrol the production of heat by said first resistance element andthereby maintain the temperature in said enclosure at a relativelyconstant level substantially equal to the transition temperature of saidpolyconductor.

3. The device as defined in claim 2 wherein said polyconductor is formedof V0 4. The device as defined in claim 2 wherein said polyconductor hasa transition temperature within the range of 10C to C.

5. The device as defined in claim 4 wherein said first resistanceelement has a value of 7 ohms, said second resistance element has avalue of 6 ohms and said polyconductor has a resistance value of 700ohms below its transition temperature.

6. A proportional temperature control device for maintaining apredetermined temperature in a chamber comprising, a source of current,an enclosure defining a chamber to be heated, a first electricalresistance element positioned within said chamber and electricallyconnected to said source of current, a polyconductor and a secondelectrical resistance element electrically connected in series to eachother and connected in parallel to said first resistance element, saidsecond resistance element being located outside of said chamber and saidpolyconductor being located inside of said chamber and formed of apolyconductive material having the characteristic that its electricalresistance value at temperatures below a predetermined transitiontemperature is at least several orders of magnitude larger than itsresistance value at temperatures above said transition temperature, saidmaterial being selected to have a resistance value below its transitiontemperature which is substantially higher than the resistance velue ofsaid first resistance element and to have a transition temperature whichis the same as the temperature which is to be maintained in saidenclosure, with the transition in resistance thereof occurringrelatively abruptly at said transition temperature over a temperaturespan of approximately 1C whereby current supplied to said firstresistance element from said current source heats said first resistanceelement in accordance with Joules law until the temperature in saidchamber reaches said transition temperature at which point saidpolyconductor becomes increasingly conductive and proportionally shuntssaid first resistance element over said 1C span thereby toproportionally control heat production by said first resistance elementand maintain said predetermined temperature in said chamber.

7. The device as defined in claim 6 wherein said second resistanceelement has a predetermined resistance value and said polyconductor hasa low resistance value above said transition temperature wherein the sumof the resistances of said polyconductor and said second resistanceelement above said transition temperature is approximately the same asthe resistance value of said first resistance element.

8. The device as defined in claim 6 including a third resistance elementlocated outside of said enclosure and connected in series between saidcurrent source and said first resistance element.

9. The device as defined in claim 6 wherein said polyconductor has atransition temperature within the range of 10C to C.

10. The device as defined in claim 9 wherein said polyconductor isformed of V0 11. The device as defined in claim 10 wherein said currentsource comprises a 6.3 volt source, said first resistance element has avalue of 7 ohms, said second resistance element has a value of 6 ohms,and said polyconductor has a resistance value of 700 ohms below itstransition temperature.

12. The device as defined in claim 7 wherein the resistance value ofsaid second resistance element is less than the resistance value of saidfirst resistance element.

13. The device as defined in claim 7 wherein the resistance value ofsaid second resistance element is greater than the resistance value ofsaid first resistance element.

1. A proportional temperature control device adapted to be connected toa source of current to produce a temperature control cycle formaintaining the temperature in an enclosure at a relatively constantlevel, said device comprising a first electrical resistance element insaid enclosure for heating the interior Of the enclosure when connectedto said source of current, a polyconductor connected in parallel withsaid first electrical resistance element in said enclosure, and a secondresistance element located outside of said enclosure and connected inseries with said polyconductor whereby, when said first resistanceelement is connected to said source of current said first resistanceelement is heated, in accordance with Joule''s law, thereby raising thetemperature within said enclosure and of said polyconductor until thetransition temperature of the latter is reached, whereupon saidpolyconductor becomes increasingly conductive and increasingly shuntssaid first resistance element to permit said first resistance element,said enclosure and said polyconductor to cool, thereby increasing theresistance of the polyconductor and allowing said first resistanceelement to produce increased heat and repeat the temperature controlcycle; said second resistance element having a resistance value which isless than that of said first resistance element, and said polyconductorbeing selected to have a resistance value below its transitiontemperature which is substantially higher than that of said firstresistance element and a resistance value above its transitiontemperature which is at least several orders of magnitude less than itshigher resistance value whereby the sum of the resistances of saidpolyconductor and said second resistance element above said transitiontemperature is comparable to the resistance value of said firstresistance element.
 2. The device as defined in Claim 1 wherein thetransition of said polyconductor from its high resistance value to itslow resistance value is abrupt, occurs over a temperature span ofapproximately 1C, and is proportional within that span, whereby theshunting of said first resistance element is proportional within saidspan to proportionally control the production of heat by said firstresistance element and thereby maintain the temperature in saidenclosure at a relatively constant level substantially equal to thetransition temperature of said polyconductor.
 3. The device as definedin claim 2 wherein said polyconductor is formed of VO2.
 4. The device asdefined in claim 2 wherein said polyconductor has a transitiontemperature within the range of 10C to 80C.
 5. The device as defined inclaim 4 wherein said first resistance element has a value of 7 ohms,said second resistance element has a value of 6 ohms and saidpolyconductor has a resistance value of 700 ohms below its transitiontemperature.
 6. A proportional temperature control device formaintaining a predetermined temperature in a chamber comprising, asource of current, an enclosure defining a chamber to be heated, a firstelectrical resistance element positioned within said chamber andelectrically connected to said source of current, a polyconductor and asecond electrical resistance element electrically connected in series toeach other and connected in parallel to said first resistance element,said second resistance element being located outside of said chamber andsaid polyconductor being located inside of said chamber and formed of apolyconductive material having the characteristic that its electricalresistance value at temperatures below a predetermined transitiontemperature is at least several orders of magnitude larger than itsresistance value at temperatures above said transition temperature, saidmaterial being selected to have a resistance value below its transitiontemperature which is substantially higher than the resistance velue ofsaid first resistance element and to have a transition temperature whichis the same as the temperature which is to be maintained in saidenclosure, with the transition in resistance thereof occurringrelatively abruptly at said transition temperature over a temperaturespan of approximately 1*C whereby current supplied to said firstresistance element from said current source heats said first resistanceelement in accordance with Joule''s law until the temperature in saidchamber reaches said transition temperature at which point saidpolyconductor becomes increasingly conductive and proportionally shuntssaid first resistance element over said 1*C span thereby toproportionally control heat production by said first resistance elementand maintain said predetermined temperature in said chamber.
 7. Thedevice as defined in claim 6 wherein said second resistance element hasa predetermined resistance value and said polyconductor has a lowresistance value above said transition temperature wherein the sum ofthe resistances of said polyconductor and said second resistance elementabove said transition temperature is approximately the same as theresistance value of said first resistance element.
 8. The device asdefined in claim 6 including a third resistance element located outsideof said enclosure and connected in series between said current sourceand said first resistance element.
 9. The device as defined in claim 6wherein said polyconductor has a transition temperature within the rangeof 10C to 80C.
 10. The device as defined in claim 9 wherein saidpolyconductor is formed of VO2.
 11. The device as defined in claim 10wherein said current source comprises a 6.3 volt source, said firstresistance element has a value of 7 ohms, said second resistance elementhas a value of 6 ohms, and said polyconductor has a resistance value of700 ohms below its transition temperature.
 12. The device as defined inclaim 7 wherein the resistance value of said second resistance elementis less than the resistance value of said first resistance element. 13.The device as defined in claim 7 wherein the resistance value of saidsecond resistance element is greater than the resistance value of saidfirst resistance element.